\documentclass[12pt,makeidx]{book}
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\usepackage{wasysym}
\usepackage{mnSymbol}%added
\usepackage{mathtools}%added
\usepackage{graphicx}%Added
\usepackage{enumitem}%Added
\usepackage[hidelinks]{hyperref}%Added
\usepackage{DotArrow}%Added
%\usepackage{metapost}%Added
\usepackage{makeidx}
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   \textheight 240mm
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%\usepackage{accents}%Added
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%\usepackage{zed-csp}%Added
%\usepackage{palatino}
%\usepackage{stmaryrd}
%\usepackage[notcite,notref]{showkeys}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\input{Declaration}
\makeindex
\begin{document}
%\input{Titlepage}
%\newpage
\pdfcatalog{/PageLayout /TwoPageLeft} %Added
%\input{Introduction}
\frontmatter
%\input{Preface}
\mainmatter
\blue
\tableofcontents
\black 
%\chapter{Background in Algebraic Geometry}
%\input{Varieties}
%\input{Schemes}
%\chapter{$\AF^1$-Homotopy Category}
%\input{Sheaves_on_Grothendieck_Topology}
%\input{Category_of_Abelian_Sheaves}
%\input{Cech_Cohomology}
%\input{Zariski_Topology}
%\input{Ramification}
%\input{Etale_Topology}
%\input{Nisnevich_Topology}
%\input{Morphisms_of_sites}
%\input{CategoriesOfNis}
%\input{SchemesOfNis}
%\input{Category_of_Sheaves}
\input{Simplicial_Sets}
\input{Model_Category}
\appendix
%\input{Categories}
%\input{Homological_Algebra}
%\input{Commutative_Algebra}
%\input{Topology}
\backmatter
%\input{Standard_Notation}
\begin{small}
%\input{Bibliography}
\end{small}
%\printindex
\end{document}
